This application is based on Japanese Patent Application No. 2000-183159 filed Jun. 19, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a swash plate type compressor of variable capacity type, and more particularly to a technique for assuring stable behavior of the swash plate which is rotated during operation of the compressor.
2. Discussion of the Related Art
One example of a swash plate type compressor of variable capacity type is disclosed in JP-A-7-91366. The compressor disclosed in the publication comprises (a) a housing having a plurality of cylinder bores formed therein such that the cylinder bores are equiangularly arranged along a circle whose center lies on a centerline of the housing; (b) a rotary drive shaft which is rotatably supported by the housing such that an axis of rotation of the rotary drive shaft is aligned with the centerline of the housing; (c) a swash plate which is carried by the rotary drive shaft such that an angle of inclination of the swash plate with respect to a plane perpendicular to the axis of rotation of the rotary drive shaft is variable, and such that the swash plate is rotated together with the rotary drive shaft; (d) a plurality of pistons which are slidably fitted in the respective cylinder bores and which engage a radially outer portion of the swash plate, each piston being reciprocated between a compression stroke end and a suction stroke end during rotation of the swash plate; and (e) a swash plate angle adjusting device for adjusting the angle of inclination of the swash plate between a maximum inclination angle and a minimum inclination angle.
The compressor further comprises an engaging protrusion which extends from a body portion of the swash plate at an angle with respect to the centerline of the body portion. The engaging protrusion has at its free end a spherical portion which is held in engagement with an engaging hole formed in a rotary member fixed to the rotary drive shaft. The swash plate has a central through-hole formed through the thickness at its central portion. The rotary drive shaft extends through the through-hole for supporting the swash plate. The configuration of the through-hole permits a tilting motion of the swash plate between a perpendicular posture in which the swash plate is perpendicular to the rotation axis of the rotary drive shaft and an inclined posture in which the swash plate is inclined by a predetermined angle with respect to the rotation axis, namely, a rotary motion of the swash plate for changing its inclination angle.
While the swash plate which is inclined with respect to the rotation axis of the rotary drive shaft is rotated, the plurality of pistons which engage the radially outer portion of the swash plate are reciprocated within the respective cylinder bores, for thereby changing the volume of the pressurizing chamber which is defined by the end face of each piston and the inner surface of the cylinder bore. Described more specifically, the volume of the pressurizing chamber is increased during a suction stroke of the piston in which a gas is sucked into the pressurizing chamber, while the volume of the pressurizing chamber is decreased during a compression stroke of the piston in which the gas is compressed. The volume of the pressurizing chamber is minimum when the piston is at its compression stroke end, and the volume of the pressurizing chamber is maximum when the piston is at its suction stroke end. The radially outer portion of the swash plate includes a compression-end circumferential part which engages each piston when each piston is at its compression stroke end, and a suction-end circumferential part which engages each piston when each piston is at its suction stroke end. Since the body portion of the swash plate generally has a circular shape, the compression-end circumferential part and the suction-end circumferential part of the swash plate are opposite to each other diametrically of the rotary drive shaft. While the swash plate which is inclined by a predetermined angle is rotated for reciprocating each piston, the swash plate receives at one of its opposite inclined surfaces the reaction force from the piston which is at its compression stroke. In this case, owing to the effect of the inclined surface, a force acts on the swash plate in a direction from its suction-end circumferential part toward the compression-end circumferential part. Accordingly, the swash plate is rotated together with the rotary drive shaft while a circumferential portion of the inner circumferential surface of the central through-hole of the swash plate, which circumferential portion is on the side of the suction-end circumferential part of the swash plate, is held in pressing contact with the corresponding circumferential portion of the outer circumferential surface of the rotary drive shaft. The above-indicated circumferential portion of the inner circumferential surface of the thorough-hole on the side of the suction-end circumferential part of the swash plate is hereinafter referred to as xe2x80x9csuction-end-side inner circumferential surfacexe2x80x9d of the through-hole.
Where the swash plate is rotated while it is placed in the substantially perpendicular posture relative to the rotation axis of the rotary drive shaft, the positions of the piston at its compression stroke end and suction stroke end in the axial direction of the rotary drive shaft are substantially identical with each other, causing substantially no change in the volume of the pressurizing chamber. Since the compression of the gas is not substantially effected in this state, the reaction force acting on the swash plate from the piston is substantially zero. In addition, the opposite surfaces of the swash plate which receive the reaction force of the piston are perpendicular to the rotation axis, in the substantially perpendicular posture of the swash plate. Accordingly, the above-indicated force acting on the swash plate owing to the effect of the inclined surface in the direction from the suction-end circumferential part toward the compression-end circumferential part of the swash plate is substantially zero or considerably small. It is, however, desirable that the suction-end-side inner circumferential surface of the through-hole of the swash plate is kept in pressing contact with the outer circumferential surface of the drive shaft by the force acting on the swash plate in the direction from its suction-end circumferential part toward the compression-end circumferential part. If the circumferential portion of the inner circumferential surface of the through-hole of the swash plate on the side of its compression-end circumferential part (hereinafter referred to as a xe2x80x9ccompression-end-side inner circumferential surfacexe2x80x9d of the through-hole) were held in pressing contact with the outer circumferential surface of the rotary drive shaft, the swash plate would be moved in its radial direction from its suction-end circumferential part toward the compression-end circumferential part during its tilting motion to increase the inclination angle. This movement causes undesirable butting noise due to a butting contact of the suction-end-side inner circumferential surface of the through-hole of the swash plate with the rotary drive shaft. Further, since the volume of the pressurizing chamber is abruptly changed due to the above-described movement of the swash plate, the discharge capacity of the compressor is also abruptly changed. To avoid these undesirable phenomena, it is preferable that the suction-end-side inner circumferential surface of the through-hole of the swash plate is always kept in pressing contact with the outer circumferential surface of the rotary drive shaft, irrespective of the inclination angle of the swash plate.
For permitting the swash plate to receive the force acting thereon in the direction from its suction-end circumferential part toward the compression-end circumferential part even while the swash plate is placed in the substantially perpendicular posture relative to the rotation axis, it is effective to design the swash plate such that the center of gravity of the swash plate is located on one side of the rotation axis of the rotary drive shaft, which one side corresponds to the compression-end circumferential part of the swash plate. The thus designed swash plate is subjected to the force acting thereon in the direction from the suction-end circumferential part toward the compression-end circumferential part, based on a centrifugal force. It is, however, desirable to minimize the magnitude of the centrifugal force because the centrifugal force deteriorates a dynamic balance of the rotating unit of the compressor.
It is an object of the present invention to provide a swash plate type compressor of variable capacity type, wherein the swash plate is rotated with the suction-end-side inner circumferential surface of the through-hole formed therein being kept in pressing contact with the outer circumferential surface of the rotary drive shaft, without deteriorating the dynamic balance of the rotating unit of the compressor.
The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A swash plate type compressor of variable capacity type comprising: a housing having a plurality of cylinder bores formed therein such that the cylinder bores are arranged along a circle whose center lies on a centerline of the housing; a rotary drive shaft which is rotatably supported by the housing such that an axis of rotation of the rotary drive shaft is aligned with the centerline of the housing; a swash plate which is carried by the rotary drive shaft such that an angle of inclination of the swash plate with respect to a plane perpendicular to the axis of rotation of the rotary drive shaft is variable, and such that the swash plate is rotated together with the rotary drive shaft; a plurality of pistons which are slidably fitted in the respective cylinder bores and which engage a radially outer portion of the swash plate, each of the pistons being reciprocated between a compression stroke end and a suction stroke end by rotation of the swash plate, the radially outer portion of the swash plate including a compression-end circumferential part which engages each piston when each piston is located at the compression stroke end; a swash plate angle adjusting device for adjusting the angle of inclination of the swash plate between a minimum inclination angle and a maximum inclination angle, and wherein the swash plate has a first center point at the maximum inclination angle and a second center point at the minimum inclination angle, each of the first and second center points being an intersection between an intermediate plane of the swash plate which is intermediate in a direction of thickness thereof and a centerline of the swash plate, (a) the first center point and the second center point being located on the axis of rotation of the rotary drive shaft, or (b) the first center point being located on the axis of rotation or offset from the axis of rotation on one side of the axis of rotation, which one side corresponds to the compression-end circumferential part of the swash plate, while the second center point is offset a larger distance from the axis of rotation than the first center point.
In the conventional swash plate type compressor of variable capacity type, the first center point of the swash plate at its maximum inclination angle is located substantially on the rotation axis of the rotary drive shaft. As the inclination angle of the swash plate gradually decreases, the center point of the swash plate is initially moved to one side of the rotation axis corresponding to the compression-end circumferential part, and then moved to the other side of the rotation axis corresponding to the suction-end circumferential part. Thus, the second center point of the swash plate at its minimum inclination angle is located on the other side of the rotation axis corresponding to the suction-end circumferential part. In the conventional compressor, the center point of the swash plate is moved so as not to offset a large distance from the rotation axis. The center of gravity of the swash plate is located on one of opposite sides of its intermediate plane, which one side is remote from the cylinder bore of the housing. Accordingly, in the conventional compressor, the second center of gravity of the swash plate at its minimum inclination angle is offset from the first center of gravity at the maximum inclination angle on the side of the suction-end circumferential part of the swash plate.
As described above, for assuring the optimum operating condition of the compressor, it is desirable to locate the center of gravity of the swash plate on one side of the rotation axis corresponding to the compression-end circumferential part, so as to cause the centrifugal force acting on the swash plate in the direction from the suction-end circumferential part toward the compression-end circumferential part while minimizing the magnitude of the centrifugal force. Further, it is desirable that the centrifugal force acting on the swash plate at the minimum inclination angle is larger than that acting on the swash plate at the maximum inclination angle. The swash plate at the maximum inclination angle receives at one of its opposite inclined surfaces the reaction force of the piston when the piston is at the compression stroke, so that the swash plate receives the force acting thereon in the direction from the suction-end circumferential part toward the compression-end circumferential part owing to the effect of the inclined surface. In contrast, the above-indicated force is substantially zero or considerably small while the swash plate is at the minimum inclination angle.
In the conventional swash plate type compressor, however, the second center of gravity of the swash plate at the minimum inclination angle is offset from the first center of gravity at the maximum inclination angle on the side of the suction-end circumferential part of the swash plate. This positional relationship between the first and second centers of gravity of the swash plate at the maximum and minimum inclination angles is contrary to the desired one. In the compressor constructed according to the present invention wherein the first and second center points of the swash plate at the maximum and minimum inclination angles are located on the rotation axis, or the first center point at the maximum inclination angle is located on the rotation axis or offset from the rotation axis on one side of the rotation axis corresponding to the compression-end circumferential part of the swash plate, while the second center point at the minimum inclination angle is offset a larger distance from the rotation axis than the first center point at the maximum inclination angle, the positional relationship between the first and second centers of gravity at the maximum and minimum inclination angles is more desirable than that of the conventional compressor described above. Accordingly, it is easier in the present arrangement than in the conventional arrangement to lower the maximum value of the centrifugal force while permitting the swash plate to receive the centrifugal force acting thereon in the direction from the suction-end circumferential part toward the compression-end circumferential part at both of the maximum and minimum inclination angles. In case where the second center of gravity at the minimum inclination angle is located on the other side of the rotation axis corresponding to the suction-end circumferential surface of the swash plate, the swash plate is subjected to a centrifugal force acting thereon in the reverse direction from the compression-end circumferential part toward the suction-end circumferential part. Even in this case, since the distance between the second center of gravity which is located on the other side of the rotation axis corresponding to the suction-end circumferential part of the swash plate and the rotation axis is smaller in the present arrangement than that in the conventional arrangement, the magnitude of the centrifugal force acting on the swash plate at the minimum inclination angle in the above-indicated reverse direction is accordingly small. Accordingly, even in this arrangement, it is easier than in the conventional arrangement to permit the suction-end-side inner circumferential surface of the through-hole of the swash plate to be kept in pressing contact with the outer circumferential surface of the rotation axis. Where the inclination angle of the swash plate at the minimum inclination is a positive value rather than zero, for instance, the swash plate receives the force acting thereon in the direction from the suction-end circumferential part toward the compression-end circumferential part, based on the reaction force of the piston at its compression stroke. If this force acting on the swash plate in the direction from the suction end side toward the compression end side is made larger than the centrifugal force acting on the swash plate in the reverse direction from the compression end side toward the suction end side; it is possible that the suction-end-side inner circumferential surface of the through-hole of the swash plate is kept in pressing contact with the outer circumferential surface of the rotary drive shaft while the swash plate is at the minimum inclination angle. Even where the inclination angle of the swash plate at the minimum inclination is zero, the suction-end-side inner circumferential surface of the through-hole of the swash plate can be kept in a pressing contact with the outer circumferential surface of the rotary drive shaft, by providing suitable biasing means such as a spring between the rotary drive shaft and the swash plate, for biasing the swash plate in the direction from the suction-end circumferential part toward the compression-end circumferential part. Thus, if the inclination angle of the swash plate at the minimum inclination is a positive value (larger than zero) or the biasing means is provided for biasing the swash plate as described above, the suction-end-side inner circumferential surface of the through-hole of the swash plate can be kept in pressing contact with the outer circumferential surface of the rotary drive shaft without employing the arrangement of the present invention. It is noted, however, that the inclination angle of the swash plate at the minimum inclination and the biasing force for biasing the swash plate in the direction from the suction-end side toward the compression-end side can be made smaller in the present arrangement.
(2) A swash plate type compressor of variable capacity type comprising: a housing having a plurality of cylinder bores formed therein such that the cylinder bores are arranged along a circle whose center lies on a centerline of the housing; a rotary drive shaft which is rotatably supported by the housing such that an axis of rotation of the rotary drive shaft is aligned with the centerline of the housing; a swash plate which is carried by the rotary drive shaft such that an angle of inclination of the swash plate with respect to a plane perpendicular to the axis of rotation of the rotary drive shaft is variable, and such that the swash plate is rotated together with the rotary drive shaft; a plurality of pistons which are slidably fitted in the respective cylinder bores and which engage a radially outer portion of the swash plate, each of the pistons being reciprocated between a compression stroke end and a suction stroke end by rotation of the swash plate, the radially outer portion of the swash plate including a compression-end circumferential part which engages each piston when each piston is located at the compression stroke end; a swash plate angle adjusting device for adjusting the angle of inclination of the swash plate between a minimum inclination angle and a maximum inclination angle, and wherein the swash plate has a first center of gravity at the maximum inclination angle and a second center of gravity at the minimum inclination angle, the first center of gravity and the second center of gravity being located on the axis of rotation of the rotary shaft or offset a substantially equal distance from the axis of rotation on one side of the axis of rotation, which one side corresponds to the compression-end circumferential part of the swash plate.
In the above mode (2) of the invention, the second center of gravity of the swash plate at the minimum inclination angle and the first center of gravity at the maximum inclination angle are offset a substantially equal distance from the axis of rotation of the rotary drive shaft. Namely, the distance between the second center of gravity at the minimum inclination angle and the rotation axis may be just equal to, slightly larger or smaller than, the distance between the first center of gravity at the maximum inclination angle and the rotation axis. The present arrangement permits the swash plate at both of the minimum inclination angle and maximum inclination angle to receive the centrifugal force acting thereon in the direction from the suction-end circumferential part toward the compression-end circumferential part while minimizing the maximum value of the centrifugal force to a required level.
(3) A swash plate type compressor of variable capacity type comprising: a housing having a plurality of cylinder bores formed therein such that the cylinder bores are arranged along a circle whose center lies on a centerline of the housing; a rotary drive shaft which is rotatably supported by the housing such that an axis of rotation of the rotary drive shaft is aligned with the centerline of the housing; a swash plate which is carried by the rotary drive shaft such that an angle of inclination of the swash plate with respect to a plane perpendicular to the axis of rotation of the rotary drive shaft is variable, and such that the swash plate is rotated together with the rotary drive shaft; a plurality of pistons which are slidably fitted in the respective cylinder bores and which engage a radially outer portion of the swash plate, each of the pistons being reciprocated between a compression stroke end and a suction stroke end by rotation of the swash plate, the radially outer portion of the swash plate including a compression-end circumferential part which engages each piston when each piston is located at the compression stroke end; a swash plate angle adjusting device for adjusting the angle of inclination of the swash plate between a minimum inclination angle and a maximum inclination angle, and wherein the swash plate has a first center of gravity at the maximum inclination angle and a second center of gravity at the minimum inclination angle, the second center of gravity being offset from the first center of gravity on the side of the compression-end circumferential part of the swash plate.
In the arrangement according to the above mode (3), the maximum value of the centrifugal force acting on the swash plate can be easily made smaller than that in the conventional arrangement while biasing the swash plate in the direction from the suction-end circumferential part toward the compression-end circumferential part at both of the minimum inclination angle and maximum inclination angle of the swash plate.
(4) A swash plate type compressor according to the above mode (3), wherein the second center of gravity is located on the axis of rotation of the rotary drive shaft or offset from the axis of rotation on one side of the axis of rotation, which one side corresponds to the compression-end circumferential part of the swash plate.
In one example according to the above mode (4), the second center of gravity of the swash plate at the minimum inclination angle is located on one side of the rotation axis of the rotary drive shaft corresponding to the compression-end circumferential part of the swash plate, while the first center of gravity at the maximum inclination angle is located on the other side of the rotation axis corresponding to the suction-end circumferential part of the swash plate.
In this arrangement, the centrifugal force acts on the swash plate in the direction from the suction-end circumferential part toward the compression-end circumferential part when the swash plate is at the minimum inclination angle where the force acting on the swash plate in the same direction owing to the effect of the inclined surface is not expected or insufficient. This arrangement is effective to stabilize the behavior of the swash plate.
In another example according to the above mode (4), the first center of gravity of the swash plate at the maximum inclination angle and the second center of gravity at the minimum inclination angle are both located on one side of the rotation axis corresponding to the compression-end circumferential part of the swash plate, and the second center of gravity is offset a larger distance from the rotation axis than the first center of gravity.
In this arrangement, the centrifugal force acts on the swash plate in the direction from the suction-end circumferential part toward the compression-end circumferential part both when the swash plate is at the minimum inclination angle and when the swash plate is at the maximum inclination angle. Further, the centrifugal force acting on the swash plate at the minimum inclination angle is larger than that at the maximum inclination angle. Accordingly, the swash plate type compressor of variable capacity type according to the present arrangement can be operated in a condition which is optimum or almost optimum from the viewpoint of the behavior of the swash plate. It is particularly desirable that the second center of gravity of the swash plate at the minimum inclination angle is offset a larger distance from the rotation axis than any other centers of gravity of the swash plate at any other inclination angles.
(5) A swash plate type compressor according to any one of the above modes (1)-(4), further comprising: a first engaging portion which is offset from the axis of rotation of the rotary drive shaft and which is rotatable together with the rotary drive shaft; and a second engaging portion which is fixed to the swash plate and which engages the first engaging portion such that the swash plate is tiltable relative to the axis of rotation of the rotary drive shaft so as to change the angle of inclination thereof, and such that the swash plate is inhibited from rotating relative to the rotary drive shaft.
The rotation of the rotary drive shaft can be effectively transmitted to the swash plate owing to the engagement of the first and second engaging portions described above.
(6) A swash plate type compressor according to the above mode (5), wherein the first engaging portion is provided on a rotary member which is fixed to the rotary drive shaft.
The first engaging portion may be provided on the rotary drive shaft. The present arrangement wherein the first engaging portion is provided on the rotary member fixed to the rotary drive shaft facilitates the installation of the first engaging portion.
(7) A swash plate type compressor according to the above mode (6), wherein the radially outer portion of the swash plate further includes a suction-end circumferential part which engages each piston when each piston is located at the suction stroke end, the suction-end circumferential part being opposite to the compression-end circumferential part diametrically of the rotary drive shaft, and wherein the rotary member has a center of gravity which is located on the axis of rotation of the rotary drive shaft or offset from the axis of rotation on the other side of the axis of rotation corresponding to the suction-end circumferential part of the swash plate.
For stable behavior of the swash plate, it is effective to locate the center of gravity of the swash plate on one side of the rotation axis of the rotary drive shaft corresponding to the compression-end circumferential part. In this case, however, the dynamic balance of the swash plate itself deteriorates to some extent. In view of this, if the center of gravity of the rotary member is located on the other side of the rotation axis corresponding to the suction-end circumferential part of the swash plate, the centrifugal force acting on the swash plate is offset or reduced by the centrifugal force acting on the rotary member. In particular, in the swash plate type compressor of variable capacity type constructed according to the above mode (2) of the invention wherein the first center of gravity and the second center of gravity are both located on one side of the rotation axis corresponding to the compression-end circumferential part of the swash plate, and the first and second centers of gravity are offset from the rotation axis by a substantially equal distance, the centrifugal force acting on the swash plate is substantially constant irrespective of the inclination angle of the swash plate. Accordingly, if the compressor is designed such that the center of gravity of the rotary member is located on the other side of the rotation axis corresponding to the suction-end circumferential part of the swash plate, and such that the magnitude of the centrifugal force acting on the rotary member is substantially equal to that acting on the swash plate, the dynamic balance of the rotating unit of the compressor including the rotary drive shaft, swash plate and rotary member can be maintained in an optimum condition irrespective of the inclination angle of the swash plate. As a result, the swash plate type compressor of variable capacity type does not suffer from undesirable vibration which would be otherwise caused by deteriorated dynamic balance of its rotation unit, regardless of its discharge capacity.
(8) A swash plate type compressor according to any one of the above modes (5)-(7), wherein the first engaging portion comprises an engaging hole having a circular shape in transverse cross section, and the second engaging portion is a protruding member which protrudes from a body portion of the swash plate such that the protruding member is inclined with respect to the intermediate plane of the swash plate, the protruding member having at a distal end thereof a spherical portion which is slidably fitted into the engaging hole of the first engaging portion.
(9) A swash plate type compressor according to any one of the above modes (1)-(8), further comprising a stopper for limiting a movement of the swash plate relative to the rotary drive shaft in a direction from the suction-end circumferential part of the swash plate toward the compression-end circumferential part of the swash plate, the stopper being formed at a portion of an inner circumferential surface of a through-hole formed through a central part of the swash plate, which portion is located on the side of the suction-end circumferential part of the swash plate, the stopper limiting the movement of the swash plate by a contact thereof with a corresponding portion of an outer circumferential surface of the rotary drive shaft.
(10) A swash plate type compressor according to the above mode (9), wherein the stopper has a curved shape in cross section in a plane which passes the compression-end circumferential part of the swash plate and the suction-end circumferential part of the swash plate and which includes the rotation axis of the rotary drive shaft.
In the swash plate type compressor of variable capacity type constructed according to any one of the above modes (1)-(4), the curved cross sectional shape and the position of the stopper are determined to satisfy the condition described in any one of the above modes (1)-(4). The curved cross sectional shape comprises an arcuate shape as defined in the following mode (11). Where the curved cross sectional shape is other than the arcuate shape, it is possible to change the position of the swash plate in a direction perpendicular to the rotary drive shaft while the stopper formed on the swash plate is held in contact with the rotary drive shaft, by appropriately changing the curved cross sectional shape of the stopper.
(11) A swash plate type compressor according to the above mode (10), wherein the curved cross sectional shape of the stopper is arcuate.
In the swash plate type compressor of variable capacity type constructed according to any one of the above modes (1)-(4), the position of the center of the arcuate shape of the stopper relative to the center point or the center of gravity of the swash plate is determined to satisfy the condition described in any one of the above modes (1)-(4).